In processing heat sensitive thermoplastic materials, it is necessary to provide for a smooth continuous uninterrupted flow to avoid thermal degradation. Extruders are designed to take into account screw, barrels, dies and cooling characteristics, attempting to utilize the best features of each to obtain the greatest efficiency in terms of output rate which may be expressed as pounds per hour. In using high output rate extruders for production, optimum efficiency is not achieved as a practical matter because the shape of the finished product may severely limit the full capacity of the extruder since the cross-sectional shape of the extrudate is small, and accordingly limits the output rate to a fraction of designed output. Further, the heating and cooling means requires considerable manipulation because the machine is running below its designed speed. In order to utilize full capacity of the extruder, adapters have been used which divide the main flow channel into a pair of flow channels which in turn are each divided further into a second pair of channels, thereby utilizing the full capacity of the extruder to its designed output efficiency. In achieving this output, the adapter apparatus introduces heating and cooling problems in the attempt to balance the flow output since the heat profile and viscosity profile is interrupted. Further these adapters require complex individual die heads to balance output.
The present invention provides a novel die head which is simple in construction utilizing the full capacity of the extruder. The die head provides a multi-strand profile output that has a balanced output without the use of valves or other mechanical flow control devices, since such control devices only add to the initial cost, upkeep and complexity of controls which results in greater cost per unit output. The present invention simplifies the controls and reduces unit cost. The present invention is particularly useful in producing shapes that require sufficient cooling as in heated PVC. An example of this is where an inside corner molding is to be produced which shape is limited to a linear rate of approximately 25 feet per minute at an output rate of 60 pounds per hours. Utilizing the apparatus of the present invention and running six shapes or outlets at a time, the production rate of 140 to 160 pounds per hour can be achieved while maintaining the same linear rate of between 20 to 30 feet per minute thereby achieving a total of between 120 to 150 feet of product per minute.